This invention relates to an exhaust gas purifying device for a marine engine and more particularly to an improved and highly effective system for treating the exhaust gases of an engine prior to their discharge to the atmosphere.
It has been known in an exhaust gas cleaning system for a two-cycle engine to utilize a plate-like catalyst arrangement disposed along the inner surface of a section of exhaust piping located between the exhaust port of the engine and a gas-water mixing area, whereat cooling water from a water jacket is mixed in with exhaust gases. Such a system gasifies lubricant oil remaining in the exhaust gases by the catalyst through oxidation or reduction reactions.
With the above-discussed cleaning system, most of the harmful constituents of the exhaust gases pass through the central portion of the exhaust piping cross-section, without contacting the plate-like catalyst. Therefore, a second catalyst is required to be disposed at an outlet end of the exhaust piping arrangement to catch such harmful constituents. However, since such a second catalyst is often disposed downstream of the gas-water mixing area, discussed above, it is located in a relatively low temperature region, which renders the catalyst less active, and accordingly, sufficient cleaning of the exhaust gases cannot be achieved.
Additionally, such systems employing multiple catalysts can be extremely cumbersome. First, such systems are often quite substantial in their spatial layout, thereby precluding the most efficient use of available space within a watercraft. Secondly, it can often be difficult accessing and replacing the catalyst members upon expiration of their useful life.
Also, exhaust gas systems which mix engine coolant with the exhaust gases along a region of an exhaust pipe system can also pose the problem of backflow of coolant toward both the catalyst, or catalysts, and also toward the exhaust ports associated with the cylinders of an engine. Such backflow is undesirable since it can render a catalyst ineffective for cleaning purposes, and it may further cause reduced engine performance.
It is therefore a principal object of this invention to provide an improved catalyst arrangement within the exhaust system of an engine for highly effective cleaning of the exhaust gases.
It is a further object of this invention to provide a catalytic exhaust gas cleaning arrangement which is readily removable from the exhaust system of an engine for easy replacement at the end of the catalyst's useful life.
It is still a further object of this invention to provide an exhaust gas arrangement which is compact in its design and is further able to prevent undesirable water coolant backflow through the exhaust system.
It is yet a further object of this invention to provide such a catalytic exhaust gas cleaning arrangement for use in a watercraft inboard-outboard motor; particularly, a four-cycle marine propulsion unit engine.